Radio sending system



Sept. 27, 1927. 1,643,781

D. G. LITTLE RADIVO SENDING SYSTEM Filed Jan. 8. 1924 v 'INVENTOR WITNESSES:

- 1 and 2 across the terminals of generator Patented Sept. 27, 1927.

UNITED STATES PATENT OFFICE.

DONALD G. LITTLE, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF'PENNSYL- VANIA.

RADIO SENDING SYSTEM Application filed" January the object of my invention is to provide means for use in connection with a radio-frequency oscillationgenerator and modulator apparatus which will prevent parasitic oscillation of modulator triodes andthereby increase the efliciency of operation of the generator in the production of modulated radio-frequency oscillations.

In the operation of high-power radio-frequency oscillation generators, using a plurality of triode thermionic discharge devices connected according to the I-Ieising constant-current modulation system, it has been found that, where several triodes are connected in parallel, difficulty is encountered because of interaction between the several triode devices which produce parasitic oscillations of an undesirable nature.

The device of my invention substantially prevents these oscillations.

Other objects and structural details of my invention will be apparent from the following description when read in connection with the accompanying drw ings, wherein:

The single figure is a diagrammatic sketch of a radio sending apparatus embodying my invention.

A plurality of thermionic discharge devices 1 and 2 are connected in parallel and energized by a generator 3. They excite an aerial system 4 to which is connected an inductance 5 and a ground 6.

Cooperating with these oscillator triodes are a plurality of modulator triodes 11 and 12 also connected in parallel, and connected as a group in parallel with oscillator triodes 3. This connection is the customary constantcurrent modulation system and the connections are completed as shown in the draw-- ing, and include a source of filament heat ing current 17.

The system of my invention comprises a radio-trequency inductance 14 connected in the parallel circuitconnection of triodes 11 and 12. The inductance 15 serves the purpose of preventing the transfer of radiofrefor increasing the 8, 1924. Serial no: 684 978;

quency oscillations from the group of oscillator triodes to the group of modulator triodes The connection between the generator 3 and the inductance 14 is made through-the choke-coil 16 to a point between the end of: inductance 15 and a tap at the center of inductance 14, as indicated in the sketch. The respective plates of triodes 11 and 12" are then connectedto the respective ends of coil 14.

Coil 14 by these connections introduces a substantial inductance into the circuits of the triodes which produces animpedancc to the flow of vibratory currents between triodes 11 and 12. It is not, however, an

impedance to vibratory currents flowing through triodes 11 and 12 in parallel, through the two halves of the coil, to the center tap connection and to the current source terminal.

Current through the triodes 11 and 12 in parallel flows through the two halves of coil 14 in op ositedirections, and the res 3ective fields t eretore neutralize each other. In consequence of this fact, coil 14 introduces no inductance into the circuit between the terminals of source 3 and vibratory currents are transmitted freely through coil 14 and triodes 11 and 12. Coil 14 further tends to equalize the current through the two triodes, since its inductive eiiect disappears only when the two currents are equal.

Under these conditions coil 14 is a noninductive connection between the triodes 11 and 12 and their supply circuits.

In the operation of my device, inductance 14 serves to stabilize the current flowing through the modulator triodes 11 and 12, and it likewise serves as a means for clamping out radio-frequency oscillations which may occur in the circuits of these triodes.

In practice, this device makes it possible to use triodes of low impedance and to operate them from an extremely high voltage source without the occurrence of parasitic oscillations in the modulator triodes, which oscillations are objectionable because of the power they waste and because of the overheating they produce in the modulator.

While I have shown only one embodiment of my invention in the accompanying drawings, it iscapable of various changes and modifications without departing from the spirit thereof, and it is desired, therefore,

that only such limitations shall be imposed thereon as are indicated in the prior art or in the appended claims.

I claim as my invention:

1. In a radio sending system, a plurality of modulator triodes having plate electrodes connected in parallel with the plate electrode of an oscillation generating tube, a

energy cooperating therewith and a radio frequency inductance connected intermediate the plates of said triodes, said energy source being connected to a midpoint of said inductance, the portions of said'inductance on either side of said mid-point neutralizing each other, whereby substantially no reactance is ofiered by said inductance to current from said source.

3. In a radio sending system, a vacuumtube oscillator, a vacuum-tube modulator, a source of direct-current energy common thereto, the modulator including a plurality of vacuum tubes arranged in parallel and an inductance in series with the plate of each tube, said inductances having a common terminal connected to saidsource of directcurrent energy and being located to produce opposing fields, Whereby they give substantially no inductive effect in the connection to said source.

In testimony whereof, I have hereunto subscribed my namethis 4th day of January 1924.

DONALD G. LITTLE. 

